Problem: $ { {-1} \times \left[\begin{array}{rrr}{-1} & {3} & {1} \\ {1} & {-2} & {3}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-1}\times{-1} & {-1}\times{3} & {-1}\times{1} \\ {-1}\times{1} & {-1}\times{-2} & {-1}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{1} & {-3} & {-1} \\ {-1} & {2} & {-3}\end{array}\right]}$